John the Baptist baptises people and Jesus grows up—he gets a visit from the magi, flees to Egypt, returns to Nazareth (all as a child), visits the Temple at 12 years old, then gets baptised by John as an adult: Matthew 2:1–23; Luke 2:41-52; Mark 1:2–8; Matthew 3:1–12; Luke 3:1–18; Mark 1:9–11; Matthew 3:13–17; Luke 3:21–22
John really did prepare the way for Jesus. He spoke to some of the same people Jesus did, and he taught some of the same themes: repentance, giving to the poor, and being honest. He even spoke to tax collectors and soldiers (two hated groups) and told them how to live to avoid ‘God’s coming wrath’. The Pharisees first heard the accusation ‘you brood of vipers’ (or snakes) from John, and the insult was later used by Jesus to address them.
‘Brood of vipers’ was a real insult. Isaiah used it to describe the terrible moral state of Judah, when people no longer looked for justice, but instead:
Isaiah 59:4-5They trust in empty words and speak lies;
They conceive evil and bring forth iniquity.
They hatch vipers’ eggs and weave the spider’s web;
He who eats of their eggs dies,
And from that which is crushed a viper breaks out.
And Jeremiah used it to describe false teachers:
Jeremiah 8:17; For behold, I will send serpents among you,
Vipers which cannot be charmed,
And they shall bite you